Driver for providing variable power to a LED array

Abstract

A driver for providing variable power to a LED array, which can be coupled through a dimmer to an AC power supply, comprises a filtering and rectifying unit, a switching power unit, and a control unit. The filtering and rectifying unit is adapted to attenuate EMI and convert an AC power from the AC power supply into a DC power output. The switching power unit is adapted to receive the DC power output and provide an output current to the LED array. The control unit is adapted to determine the output current in response to a comparison between a dim reference signal representing phase-modulating information of the AC power and a feedback signal representing an average value of the output current. The LED array can thus be controlled by a dimmer at the primary side so as to adjust its light output, and can further be utilized in currently existing lighting infrastructures.

The invention claimed is: 
     
       1. A driver for providing variable power to at least one LED array when coupled through a phase-modulating dimmer to an AC power supply, the driver comprising:
 a filtering and rectifying unit for attenuating electromagnetic interference from/to the AC power supply and converting an AC power from the AC power supply into a DC power output; 
 a switching power unit for receiving the DC power output from the filtering and rectifying unit and providing an output current to the LED array; and 
 a control unit for determining the output current to the LED array in response to a comparison between a dim reference signal representing phase-modulating information of the AC power when the phase angle of the AC power is cut by the phase-modulating dimmer and a feedback signal representing an average value of the output current to the LED array, wherein the control unit comprises a first sampling sub-unit adapted to sample the dim reference signal and cause the dim reference signal to be in a low frequency range, and a second sampling sub-unit adapted to sample the feedback signal and cause the feedback signal to be in a low frequency range. 
 
     
     
       2. The driver according to  claim 1 , wherein the dim reference signal is approximately a flat voltage signal. 
     
     
       3. The driver according to  claim 1 , wherein the feedback signal is kept in a voltage waveform in accordance with a current waveform of the output current to the LED array, 
     
     
       4. The driver according to  claim 1 , wherein the cross-over frequency of the control unit is lower than 50 HZ. 
     
     
       5. The driver according to  claim 4 , wherein the cross-over frequency is lower than 15 HZ. 
     
     
       6. The driver according to  claim 1 , wherein the switching power unit is arranged in a single-stage configuration and comprises a flyback transformer. 
     
     
       7. The driver according to  claim 1 , wherein the control unit comprises a third sampling sub-unit adapted to sample a voltage signal reflecting a voltage waveform of the AC power, and wherein the control unit is adapted to implement a power factor correction in response to the voltage signal. 
     
     
       8. A lighting device comprising at least one LED array and a driver according to  claim 1 . 
     
     
       9. A method of providing variable power to at least one LED array, the method comprising the steps of:
 supplying current to the LED array by means of a power supply; and 
 adjusting the current in accordance with a dimming demand signal at an input side of the power supply, by performing a comparison between a dim reference signal representing phase-modulating information at the input side of the power supply and a feedback signal representing an average value of the current to the LED array, wherein the adjusting step comprises a first sub-step of sampling and low-pass filtering the dim reference signal, and a second sub-step of sampling and low-pass filtering the feedback signal. 
 
     
     
       10. The method according to  claim 9 , wherein the adjusting step is further based on a voltage signal reflecting the voltage waveform at the input side of the power supply for acquiring a power factor correction. 
     
     
       11. A driver for providing variable power to at least one LED array when coupled through a phase-modulating dimmer to an AC power supply, the driver comprising:
 a filtering and rectifying unit for attenuating electromagnetic interference from/to the AC power supply and converting an AC power from the AC power supply into a DC power output; 
 a switching power unit for receiving the DC power output from the filtering and rectifying unit and providing an output current to the LED array; and 
 a control unit for determining the output current to the LED array in response to a comparison between a dim reference signal representing phase-modulating information of the AC power when the phase angle of the AC power is cut by the phase-modulating dimmer and a feedback signal representing an average value of the output current to the LED array, wherein the control unit comprises a third sampling sub-unit adapted to sample a voltage signal reflecting a voltage waveform of the AC power, and wherein the control unit is adapted to implement a power factor correction in response to the voltage signal. 
 
     
     
       12. The driver according to  claim 11 , wherein the dim reference signal is approximately a flat voltage signal. 
     
     
       13. The driver according to  claim 11 , wherein the feedback signal is kept in a voltage waveform in accordance with a current waveform of the output current to the LED array, 
     
     
       14. The driver according to  claim 11 , wherein the cross-over frequency of the control unit is lower than 50 HZ.